The Sui dynasty (581–618), which reunified China after nearly four centuries of political fragmentation during which the north and south had developed in different ways, played a part far more important than its short span would suggest. In the same way that the Qin rulers of the 3rd century bc had unified China after the Zhanguo (Warring States) period, so the Sui brought China together again and set up many institutions that were to be adopted by their successors, the Tang. Like the Qin, however, the Sui overstrained their resources and fell. And also as in the case of the Qin, traditional history has judged the Sui somewhat unfairly, stressing the harshness of the Sui regime and the megalomania of its second emperor and giving too little credit for its many positive achievements.

Wendi (reigned 581–604), the founder of the Sui dynasty, was a high-ranking official at the Bei (Northern) Zhou court, a member of one of the powerful northwestern aristocratic families that had taken service under the successive non-Chinese royal houses in northern China and had intermarried with the families of their foreign masters. In 577 the Bei Zhou had reunified northern China by conquering the rival northeastern dynasty of Bei Qi. However, political life in the northern courts was extremely unstable, and the succession of an apparently deranged and irresponsible young emperor to the Zhou throne in 578/579 set off a train of court intrigues, plots, and murders. Wendi was able to install a child as puppet emperor in 579 and seize the throne for himself two years later.

In control of all of northern China and in command of formidable armies, he immediately set about establishing order within his frontiers. He built himself a grand new capital, Daxing, close to the site of the old Qin and Han capitals, a city erected quickly with a prodigal use of compulsory labour. This great city remained (later under the name Chang’an) the capital of the Sui and Tang dynasties and the principal seat of government until the beginning of the 10th century.

Wendi also took quick action to protect the frontiers of his new state. China during the 6th century had a formidable northern neighbour in the Turks (Tujue), who controlled the steppe from the borders of Manchuria to the frontiers of the Byzantine and Sāsānian empires. At the time of Wendi’s seizure of power, the Turks were splitting into two great empires, an eastern one dominating the Chinese northern frontier from Manchuria to Gansu and a western one stretching in a vast arc north of the Tarim Basin into Central Asia. Wendi encouraged this split by supporting the khan (ruler) of the western Turks, Tardu. Throughout his reign Wendi also pursued a policy of encouraging factional strife among the eastern Turks. At the same time, he strengthened his defenses in the north by repairing the Great Wall. In the northwest in the area around the Koko Nor (Qinghai Hu; “Blue Lake”), he defeated the Tuyuhun people, who from time to time raided the border territories.

By the late 580s Wendi’s state was stable and secure enough for him to take the final step toward reunifying the whole country. In 587 he dethroned the emperor of the Hou (Later) Liang, the state that had ruled the middle Yangtze valley as a puppet of the Bei Zhou since 555. In 589 he overwhelmed the last southern dynasty, the Chen, which had put up only token resistance. Several rebellions against the Sui regime subsequently broke out in the south, but these were easily quelled. Wendi now ruled over a firmly reunited empire.

Wendi’s institutional reforms

Wendi achieved much more than strengthening and reunifying the empire. He provided it with uniform institutions and established a pattern of government that survived into the Tang dynasty and beyond. A hardworking administrator, he employed a number of extremely able ministers who combined skill in practical statecraft with a flexible approach to ideological problems. They revived the Confucian state rituals to win favour with the literati and to establish a link with the empire of the Han, and, at the same time, they fostered Buddhism, the dominant religion of the south, attempting to establish the emperor’s image as an ideal Buddhist saint-king.

Wendi’s lasting success, however, was in practical politics and institutional reforms. In the last days of the Bei Zhou, he had been responsible for a revision of the laws, and one of his first acts on becoming emperor was to promulgate a penal code, the New Code of 581. In 583 his ministers compiled a revised code, the Kaihuang Code, and administrative statutes. These were far simpler than the laws of the Bei Zhou and were more lenient. Considerable pains were taken to ensure that local officials studied and enforced the new laws. Toward the end of Wendi’s reign, when neo-Legalist political advisers gained ascendancy at court, the application of the laws became increasingly strict. The Kaihuang code and statutes have not survived, but they provided the pattern for the Tang code, the most influential body of law in the history of East Asia.

The central government under Wendi developed into a complex apparatus of ministries, boards, courts, and directorates. The conduct of its personnel was supervised by another organ, the censorate. The emperor presided over this apparatus, and all orders and legislation were issued in his name. He was assisted by the heads of the three central ministries who acted as counselors on state affairs (yiguozheng). That system later provided the basic framework for the central government of the early Tang.

Even more important, he carried out a sweeping reform and rationalization of local government. The three-level system of local administration inherited from Han times had been reduced to chaos during the 5th and 6th centuries by excessive subdivision; there were innumerable local districts, some of them extremely small and dominated by single families. Wendi created a simplified structure in which a much reduced number of counties was directly subordinated to prefectures. He also rationalized the chaotic rural administrative units into a uniform system of townships (xiang). Appointments to the chief offices in prefectures and counties were now made by the central government rather than filled by members of local influential families, as had been the practice. This reform ensured that local officials would be agents of the central government. It also integrated local officials into the normal pattern of bureaucratic promotion and in time produced a more homogeneous civil service.

Since the registration of population had fallen into chaos under the Bei Zhou, a careful new census was carried out during the 580s. It recorded the age, status, and landed possessions of all the members of each household in the empire, and, based on it, the land allocation system employed under the successive northern dynasties since the end of the 5th century was reimposed. The tax system also followed the old model of head taxes levied in grain and silk at a uniform rate. The taxable age was raised, and the annual period of labour service to which all taxpayers were liable was reduced.

Wendi’s government, in spite of his frontier campaigns and vast construction works, was economical and frugal. By the 590s he had accumulated great reserves, and, when the Chen territories were incorporated into his empire, he was in a position to exempt the new population from 10 years of taxes to help ensure their loyalty.

The military system likewise was founded on that of the northern dynasties, in which the imperial forces were organized into militias. The soldiers served regular annual turns of duty but lived at home during the rest of the year and were largely self-supporting. Many troops were settled in military colonies on the frontiers to make the garrisons self-sufficient. Only when there was a campaign did the costs of the military establishment soar.

Integration of the south

The second Sui emperor, Yangdi (reigned 604–617/618), has been depicted as a supreme example of arrogance, extravagance, and personal depravity who squandered his patrimony in megalomaniac construction projects and unwise military adventures. This mythical Yangdi was to a large extent the product of the hostile record written of his reign shortly after his death. His reign began well enough, continuing the trends begun under Wendi; a further revision of the law code that generally reduced penalties was carried out in 607.

Yangdi’s principal achievement was the integration of the south more firmly into a unified China. There is little evidence that the south was ever completely brought into line with all the administrative practices of the north; the land allocation system seems unlikely to have been enforced there, and it is probable that the registration of the population, the essential foundation for the whole fiscal and military system, was only incompletely carried out in the old Chen territories. However, Yangdi himself was personally heavily involved with the south. Married to a princess from the southern state of Liang, he had spent 591–600 as viceroy for the southern territories; their successful integration into the Sui empire after the initial wave of risings was largely because of his administration and the generally clement policies employed in the former Chen territories.

His identification with the southern interest was one of the reasons he began establishing an examination system, based upon the Confucian Classical curriculum, as a means of drawing into the bureaucracy scholars from the southern and northeastern elites who had preserved traditions of Confucian learning. Hitherto, the court had been dominated by the generally less cultivated aristocratic families of mixed ancestry from northwestern China.

Yangdi also attempted to weaken the predominance of the northwest by building a second great capital city at Luoyang, on the border of the eastern plains. This capital was not only distant from the home territories of the northwestern aristocrats but also easily provisioned from the rich farmlands of Hebei and Henan. The new city was constructed in a great hurry, employing vast numbers of labourers both in building and in transporting the timber and other materials required. Yangdi also built new palaces and an immense imperial park, again with a prodigal use of labour.

Another grandiose plan aimed at unifying the empire was to develop still further the canal system his father had begun in the metropolitan region and to construct a great waterway, the Bian Canal, linking Luoyang with the Huai River and with the southern capital, Jiangdu (present-day Yangzhou), on the Yangtze. Much of this route followed existing rivers and ancient canals, but it was still an immense undertaking that employed masses of forced labourers working under appalling conditions. In 605 the canal system was opened between the capital at Luoyang and the Yangtze, and in 610 it was extended south of the Yangtze to Hangzhou as part of a general effort to rehabilitate and lengthen the Grand Canal. At the same time, in preparation for campaigns in Manchuria and on the Korean frontier, another great canal was built northward from Luoyang to the vicinity of modern Beijing. By 611 the entire eastern plain had a canal system linking the major river systems of northern China and providing a trunk route from the Yangtze delta to the northern frontier. The construction of these waterways was inordinately expensive, caused terrible suffering, and left a legacy of widespread social unrest, but in the long term the transportation system was to be a most important factor for maintaining a unified empire. Further hardship was caused by the mass levies of labour required to rebuild and strengthen the Great Wall in Shanxi in 607 and 608 as a precaution against the resurgent eastern Turks.

Perceptions of China, a country in East Asia, must be adjusted to its enormous scale. Its culture and its civilization go back thousands of years. Its vast area is the third largest in the world, after Russia and Canada, and China is Earth’s most populated country. Area 3,696,100 square miles (9,572,900 square kilometers). Population (2015 est.) 1,370,708,000.